Microsoft Defender's Own Driver Can Be Weaponized to Delete Security Software at Boot
Security researchers have discovered a method to weaponize a legitimate Microsoft Defender driver, BTR.sys, to perform unauthorized file and registry operations. The technique allows for the deletion of security software at the boot level, though no real-world exploitation has been observed.
Why it matters
This vulnerability highlights the risks associated with 'living-off-the-land' attacks, where legitimate system tools are repurposed by malicious actors to bypass security measures.
Check Point Research has disclosed a technique that uses Microsoft Defender's own legitimately signed boot-time remediation driver to perform arbitrary kernel-level file and registry operations on Windows systems ranging from Windows 7 through Windows 11 25H2, with no software flaw exploited and no driver imported from outside the machine.
The driver, BTR.sys (Boot Time Removal Tool), is a required Windows component, which means it cannot be added to Microsoft's Vulnerable Driver Blocklist or blocked via Windows Defender Application Control (WDAC) without disrupting Defender itself.
Jiří Vinopal, a threat researcher and reverse engineer at Check Point Research, presented the findings as a main-stage briefing at Black Hat USA 2026 and DEF CON 34 in Las Vegas and published the accompanying research paper alongside a proof-of-concept tool, BTR_CLI, on August 20, 2026. Check Point Research said it found no evidence the technique has been used in real-world attacks.
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